1. Field of the Invention
The present invention generally relates to methods and circuits for restoring a drooped DC signal, and, in particular, methods and circuits for restoring a drooped DC signal using both asynchronous and synchronous methods.
2. Description of the Prior Art
A DC signal may have both positive and negative amplitudes. As a DC signal travels from a transmitter to a receiver via a long medium (such as a cable), if the DC signal is not balanced, the signal will droop as it travels through a transformer. This situation is also know as base-line wander. For example, referring to FIG. 1a, a transmitter 10 is connected to a transformer 15 and out to a cable 14. On the other end of the cable 14, there is another transformer 17 connected to a receiver. Drooping occurs after both transformers. At node A 16, a point near the transmitter 10, as is illustrated by FIG. 1b, there is almost no drooping. After passing through the transformers, 15 and 17, at a point near the receiver 12, node B 18, there may be significant dropping as is illustrated by FIG. 1c. Note that the illustrated signal waveforms are MLT3 signals used in network protocols. The present invention as is disclosed below is not limited to MLT3 signals.
In a drooping situation, both the positive amplitude and the negative amplitude drifts toward zero volt. In order to properly process the received signal, a receiver should restore the signal before further processing the signal. Otherwise, the equalizer cannot generate the correct results. Therefore, it is desirable to have methods and circuit for restoration of a drooped signal.